Dennis N. Smith

Mercury Measurement and Its Control: What We Know, Have Learned, and Need to Further Investigate

The U.S. Department of Energy (DOE), through the Federal Energy Technology Center (FETC), manages the largest funded program in the country for developing (1) an understanding of mercury emissions, (2) measurement of these emissions, and (3) control technology (-ies) for these emissions for the U.S. coal-fired electric generating industry. DOE has initiated, or has collaborated with other government and industrial organizations in, these and other efforts relating to mercury and other hazardous air pollutants (HAPs), also known as air toxics. One of DOEs first reports on trace elements in coal was conducted from 1976 through 1978 by researchers at DOEs Pittsburgh Energy Technology Center (PETC, now FETC) and the Pittsburgh Mining Operations of the Department of the Interiors Bureau of Mines. The report was completed less than two years after DOE was formed, and 13 years before Title III of the 1990 Clean Air Act Amendments was enacted (Cavallaro et al., March 1978).

Dispersed solid dynamics in a slurry bubble column

Abstract New data and theory are presented for describing dispersed solids in slurry bubble columns. Axial solids concentration distributions were measured in a 0.108 m.i.d. slurry bubble column apparatus operated at steady-state conditions. Slurry and gas superficial velocities ranged from 0.0 to 0.02 m/s and 0.03 to 0.20 m/s, respectively. The liquid-phase was either water or ethanol, and the solid-phase consisted of narrow-sized fractions of glass spheres. With a one-dimensional sedimentation-dispersion model, the data have been used to develop a method for predicting average solids loading and axial distribution of solids in a bubble column. Correlations are given for the hindred settling velocity, the solids dispersion coefficient, and the solids concentration at the top and bottom of the column. A solids distribution function is derived using one parameter that contains the hindred settling velocity and the solids dispersion coefficient. The new method is applied to data from the literature for three slurry bubble columns with diameters in the range of 0.066–0.286 m. The new method predicts axial distribution of solids with improved accuracy over existing methods, especially for non-aqueous systems and for those with low slurry feed concentration or high settling velocity.

Control of mercury emissions from coal-fired power plants: a preliminary cost assessment and the next steps for accurately assessing control costs

Abstract Mercury emissions from coal-fired power plants have been extensively evaluated for nearly 10 years to determine possible regulation by the Environmental Protection Agency (EPA). Under a court order, a determination will be made on whether it is appropriate and necessary to regulate toxic air pollutant emissions (focusing on mercury) from coal-fired utility boilers by December 15, 2000. If it is determined that regulations are necessary, then the regulatory process will have a fixed timetable. A proposed regulation will be due no later than December 15, 2003, and promulgated no later than December 15, 2004. The utility industry regulatory compliance must be in place by December 2007 since the Clean Air Act requires that sources come into compliance with Maximum Achievable Control Technology (MACT) 3 years after promulgation of the regulations. While it is recognized that the main driver for regulation is the potential risk to human health and that this risk is currently being examined by a number of health-based organizations, the actual form of any regulation would likely be dependent upon the availability of cost-effective control technologies. Furthermore, the diverse nature of the coal-fired utility industry will likely limit the applicability and cost-effectiveness of any given technology for the current boiler population. In light of a potential regulatory determination, this paper examines a few control options that warrant further consideration. A preliminary assessment of mercury capture technologies and associated costs is conducted for sorbent injection technology. Sorbent-based technologies that may be amenable for mercury control include: (1) sorbent injection with and without spray cooling upstream of existing particulate control devices (i.e., electrostatic precipitators and fabric filters); and (2) sorbent injection with and without spray cooling associated with additional control devices designed to augment particulate collection in a primary particulate control device. Important design criteria for each of the control systems are critically assessed for operability, maintainability, and reliability, with the projected impacts of the control system on power plant operations being evaluated. The sorbent-based technology discussed in this paper focuses on the injection of activated carbon associated with the various particulate control devices used in the utility industry. The paper also addresses the next steps and revisions needed to accurately assess possible cost impacts to the utility industry as the mercury control options mature in their development.

AN ASSESSMENT OF EXPERIMENTAL TECHNIQUES FOR THE MEASUREMENT OF BUBBLE SIZE IN A BUBBLE SLURRY REACTOR AS APPLIED TO INDIRECT COAL LIQUEFACTION

The proper design and control of an indirect coal liquefaction process plant require an accurate knowledge of bubble sizes and size distribution. Of particular importance regarding proper design is the understanding of the complicated dependence of bubble dynamics on bubble column geometry, and of the nature of the solid-liquid phases. The nature of the products and their relative proportions, on the other hand, are seriously influenced by the bubbling characteristics of the reactor because the mass transfer behavior and mixing are dependent on the bubble size and velocity distributions. This report reviews experimental techniques that have been employed to measure bubble sizes in multiphase reactors. The methods, which fall in three different categories, namely, the photographic method, the optical probe, and the electrical conductivity (resistivity) probe, are described in a historical sequence; and in each case, their unique features and design details are discussed. A general methodology of data analy...

MATHEMATICAL MODELING OF FISCHER- TROPSCH SLURRY BUBBLE COLUMN REACTORS

Three-phase slurry bubble column reactors are used in a wide variety of biological and chemical operations. This work is a comprehensive review of the mathematical modeling of such reactors for the Fischer-Tropsch (F-T)synthesis as applied to indirect coal liquefaction. The salient features of the F-T slurry bubble column reactors are described, and the fundamental mass transfer and kinetic rate processes that are needed to model the reactor performance are discussed. A brief description of the F-T chemistry, including principal F-T reactions, properties of commonly used F-T catalysts, and the Schulz-Flory distribution, is also given. All of the mathematical models for the F-T slurry process that have been developed to date are presented in enough detail to highlight the basic relations as well as the implicit assumptions. The refinements introduced by different workers are emphasized, as well as the numerical results obtained from these models either in the perspective of comparison with experimental dat...

THERMAL DISPERSION AND HEAT TRANSFER IN NONISOTHERMAL BUBBLE COLUMNS

Abstract Local axial and radial temperatures were measured at steady-state conditions in a 0.078-m-I.D. bubble column heat exchanger. Nitrogen and water superficial velocity ranges were 0-0.6 m/s and 0-0.02 m/s, respectively. Average column pressures were 3.0, 5.1, and 7.1 atm. The axial temperature profile varied significantly with all conditions encountered. Radial temperature profiles were found to be nearly constant, indicating very good radial mixing. An axial thermal dispersion heat transfer model, capable of representing nonisothermal systems, was employed to characterize the measured bubble column temperature profiles. Thermal dispersion was apparent from large temperature changes in the entrance of the bubble column. Heat transfer coefficients depended on the gas and liquid flow rates. However, the thermal dispersion coefficients depended on linear gas velocity and were a weak function of liquid flow rates. The thermal dispersion coefficients obtained in this study were found to be consistent wit...

Preliminary estimates of performance and cost of mercury control technology applications on electric utility boilers.

ABSTRACT Under the Clean Air Act Amendments of 1990, the U.S. Environmental Protection Agency (EPA) determined that regulation of mercury emissions from coal-fired power plants is appropriate and necessary. To aid in this determination, preliminary estimates of the performance and cost of powdered activated carbon (PAC) injection-based mercury control technologies were developed. This paper presents these estimates and develops projections of costs for future applications. Cost estimates were developed using PAC to achieve a minimum of 80% mercury removal at plants using electrostatic precipitators and a minimum of 90% removal at plants using fabric filters. These estimates ranged from 0.305 to 3.783 mills/kWh. However, the higher costs were associated with a minority of plants using hot-side electrostatic precipitators (HESPs). If these costs are excluded, the estimates range from 0.305 to 1.915 mills/kWh. Cost projections developed using a composite lime-PAC sor-bent for mercury removal ranged from 0.183 to 2.270 mills/kWh, with the higher costs being associated with a minority of plants that used HESPs.Under the Clean Air Act Amendments of 1990, the U.S. Environmental Protection Agency (EPA) determined that regulation of mercury emissions from coal-fired power plants is appropriate and necessary. To aid in this determination, preliminary estimates of the performance and cost of powdered activated carbon (PAC) injection-based mercury control technologies were developed. This paper presents these estimates and develops projections of costs for future applications. Cost estimates were developed using PAC to achieve a minimum of 80% mercury removal at plants using electrostatic precipitators and a minimum of 90% removal at plants using fabric filters. These estimates ranged from 0.305 to 3.783 mills/kWh. However, the higher costs were associated with a minority of plants using hot-side electrostatic precipitators (HESPs). If these costs are excluded, the estimates range from 0.305 to 1.915 mills/kWh. Cost projections developed using a composite lime-PAC sorbent for mercury removal ranged from 0.183 to 2.270 mills/kWh, with the higher costs being associated with a minority of plants that used HESPs.

Supply curves for using powder river basin coal to reduce sulfur emissions

Abstract Supply curves were prepared for coal-fired power plants in the contiguous United States switching to Wyomings Powder River Basin (PRB) low-sulfur coal. Up to 625 plants, representing ∼44% of the nameplate capacity of all coal-fired plants, could switch. If all switched, more than

Explosive comminution of bituminous coal using steam

8.8 billion additional capital would be required and the cost of electricity would increase by up to

Modified sedimentation-dispersion model for solids in a three-phase slurry column

5.9 billion per year, depending on levels of plant derating. Coal switching would result in sulfur dioxide (SO2) emissions reduction of 4.5 million t/yr. Increase in cost of electricity would be in the range of 0.31-0.73 cents per kilowatt-hour. Average cost of S emissions reduction could be as high as